Electromagnetic relay



,July 15, 1941; N, F. AGNEW 2,249,104

ELECTROM AGNET I C RELAY Filed Sept. 19, 1959 Pick Au Vzfag/ nsulaon.

INV ENTOR lfrom an inspection of this voltage at which an uncompensated relay Patented July 15, 1941 UNITED sTATEs PATENT OFFICE ELECTROMAGNETIC RELAY Norman F. Agnew,

Wilkinlbnrg, Pa., assignor to The Union Switch a Signal Company, Swissvale, Pa., a corporation o! Pennsylvania Application September 19, 1939, Serial No. 295,619

2 Claims.

vision of electromagnetic vrelays incorporating novel and improved means for varying the magnitude of the tractive iorce required to operate the relays in accordance with variationsin the ambient temperature.

Another object of my invention is the provision, in an electromagnetic relay, of novel and improved means for varying an air gap in the relay magnetic circuit in accordance with variations in ambient temperature in such manner (ci. 11s-ass) as to provide inverse straight line operating characteristics for the relay over a wide range of ambient temperature.

Other objects and advantages of my invention will appear from the following description.

I shall describe one form of apparatus embodylng my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, in which curveA a illustrates the manner that the voltage characteristics of an uncompensated relay are affected by variations in ambient temperature; Curves b and c illustrate, respectively,

the voltage characteristics of a partially compensated relay and a relay compensated in accordance with my invention. Fig'. 2 is a diagrammatic view of 4a preferred form of electromagnetic relay embodyingmy invention.

Referring first to curve a of Fig. l, which illustrates the voltage characteristics o! an uncompensated electromagnetic relay, it is evident curve that the applied picks up is directly proportional to the ambient temperature. This is due to the fact that the copper winding ordinarily employed in a relay has a positive temperature coeiiicient, so that an increase in ambient temperature causes a corresponding increase in resistance of the winding with the result that for a constant applied volt- Fig. l is a graph age, the current iiow decreases. In order, therefore, to obtain the tractive force` necessary to operate the relay armature. the voltage applied to the relay must be increased as the ambient temperature increases.

At times, however, it is desirable to employ a relay which picks up at a higher voltage at low temperatures than it does at high temperatures, or in other words, a relay having the characteristics of inversely varying its pick-up voltage with ambient temperature variations. This type voi relay is particularly suitable for use in two-rate battery charging systems, such, for example. as illustrated in United States Letters Patent No. 1,885,908, granted to R. M. Gilson on November 1, 1932, since it is a well recognized fact that the terminal voltagevof storage batteries varies inversely with ambient temperatures.

It is known that a particularly effective means for compensating relays for ambient temperature is to vary the length of an air gap interposed in the relay magnetic circuit in accordance with. ambient temperature variations. Heretoiore, ambient temperature compensation has been obtained by utilizing the linear deflection of a thermally responsive element to produce corresponding linear variations in the length of the armature air gap. This method provides only partial compensation for ambient temperature, as can be seen from the fact that the tractive force exerted by an electromagnet on its armature varies inversely as the square oi the length of the amature air gap, the force being represented by the formula este where F=iorce in pounds B=crosssectional area of core in square inches N=number of turns of winding I :current in amperes l :length of air gap in inches c :a constant The voltage characteristics of a typical relay compensated in the above manner is illustrated in curve b of Fig. 1, from which curve it can be seen that the pick-up voltage of the relay remains substantially constant throughout the lower half o! the temperature range but drops sharply in the upper half of the range.

In order. therefore, to provide a relay having inverse straight line operating characteristics over a wide range of ambient temperature. I propose to improve the control established by the It follows that by properly proportioning cam linear deflections of a thermally responsive elei6 and thermally responsive element il. any dement over an air gap interposed in the relay sired voltage characteristic can be provided for magnetic circuit. Referring now to Fig. 2, the relay R. Thus, for example, the surface of cam reference character R. designates a relay embody- 5 l. can be so selected that the armature opening ing my invention. As shown. relay R. comprises of relay Ris varied in such manner that the relay a U-shape frame 5 having a magnetizable core i will pick up at a constant voltage regardless of connectedtheretoinasuitablemanner,asbymeans variations in ambient temperature, or, by changof ascrew 1. Mounted' on core 6 is amagnetizing ing the surface of cam il, the relay can be dewinding 8, which ordinarilyisconstructed of copl signed to have a straight line pick-up voltage per wire and which possesses a positive temperacharacteristic inversely proportional to ambient ture coefficient of resistance. An armature l protemperature, similar for example, to curve c of vided for the electromagnetic relay is pivotally Fig. 1. mounted at il and normally occupies a retracted An advantage ot a relay embodying my invenposition by virtue or the weight and spring torce 1s tion is that uniform regulation is obtained over e of a contact member I2 which is operatively eonwide range of ambient temperature, thus pernecd with x-mature g, A, shown, .contact mitting the construction of relays having straight member i2 engages another contact member il line Voltage characteristics substantially similar to form a circuit controlling contact -ll, to the voltage characteristics of storage batteries. which contact is opened whenever winding 8 is 20 end providing relay hiwins improved voltage energized sufficiently to attract amature l to its characteristics suitable for use in two-rate batattracted position. te?? Chllins lysms Relay R, further comprises a thermally respon- Although I have herein shown and described sive element I here shown in the form of a biolily one 10m 0f eleeti'mnetie relay embodymetallic strip formed of two metals having dineri118 my invention', it is understood that various ent coemcients 0f thermal expansion, Thg therchanges and modictlOIiS may be made therein many responsive element is incorporated into within the scope of the appended claims without relay R by rigidly securing one of its ends and deprtlns from the spirit and scope of my invenpoeitioning the other or free end or the element tion. in such manner as to engage armature l to limit Having thus described my invention, what the movement of the amature to its retracted I 6mm 1S: position. The eiement is is arranged to deneot i. A relay comprising. in combination, an elecdownwardly from its illustrated position as the tromanet. n DiVOffedsrmnturemountedformovetemperature increases and to deiiect upwardly as ment relative to said electromagnet and biased the temperature decreases, It i.; readily .ppmtherefrom. a thermally responsive element having ent that as the free end of element Ii detiects a surface which moves with temperature chenses due to variations in ambient temperature, the transversely to the line of motion of said armaposition'at which element il engages armature ture, and a cam surface formed on said armature s is altered due to the deflection in the element and cooperating with said moviniir surface or said to thereby vary the length of the air gap between 40 thermally responsive element for limiting the the pole piece of core l and amature l, and as movement of said armature relative to said eleca result the tractive force required to operate tromagnet, said cam surface being shaped the armatureto its attracted positionisvaried. throughout to provide seid relay with a linear Relay R additionally includes suitable means temperature-voltage characteristic throughout a for modifying the control established by thermal. v relatively wide range of ambient temperatures. 1y responsive element Il over the armature air o 2. A relay comprising an electromagnet and gap. Ashere shown, such modifying means coman armature mounted for movement relative to prises a cam IB formed on the rear face of armasaid electromagnet and biased therefrom, a cam ture I and disposed to be engaged by the free end provided on said armature and a thermostatic of the thermally responsive element. The shape element having a. surface which moves with temof cam it is so designed with respect to the denec- Peinture 011311888 tlnsvei'sely to the line of motion of element il due to ambient temperature tion of said amature, said cam having a surface variations that the free end of the element enensaseable by said surface oi' said thermostatic gages the surface of cam II to permit a predeelement and shaped throughout to cooperate with termined amount of movement of the armature u said surface of said thermostatic element to protoward or away from core I in accordance with vide said relay with linear temperature-voltage the predetermined decrease or increase in amcharacteristics.

bient temperature. NORMAN F. AGNEW. 

